<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .a{background:blue;width:220px;height: 220px;}
        .a{border-radius: 110px}
    </style>

</head>
<body>
<div class="a"></div>

</body>
</html>